Abstract
Purpose :
When fixating a target, small eye movements (drift, microsaccades and tremors) cause the eyes to move. We have devised a novel fixation target (a radial sine wave grating) that, when drifting, recruits optokinetic-like responses. We predict that these drift-induced eye movements will either stabilize (contracting) or destabilize (expanding) fixation.
Methods :
Five typical observers with normal vision were asked to fixate four different fixation targets for 90s each in random order. The target was either a radial sine wave luminance grating (3° diameter; 1 cpd; 100% contrast) that contracted (2Hz), expanded (2Hz) or was stationary (0Hz). As a control condition, observers fixated a ‘bull’s eye and cross hair’ target (0.6° outer diameter; 0.2° inner diameter) previously reported to improve fixation performance (Thaler et al. 2013). All stimuli were presented against a 53 cd/m2 mean luminance grey background. Observers viewed the targets binocularly and eye movements were recorded at 1000Hz from the eye with better acuity. Saccades and blinks were excluded from eye movement traces and a bivariate probability density function of target-relative eye position was calculated. The accuracy and precision of gaze were derived from the 68% isocontour that encompassed the eye position data.
Results :
There was a significant main effect of stimulus type on the accuracy of eye position [F(3,12) = 5.979, p = 0.010, η2 = 0.599]. The contracting stimulus resulted in more accurate fixation than the typical bull’s eye and crosshair stimulus (pbonf = 0.009). There were no other significant differences among the different stimuli for fixation stability. Despite our novel fixation target being larger in diameter, there was no significant change in precision compared to the conventional target.
Conclusions :
Our results suggest that our novel contracting concentric fixation targets improve the accuracy of fixation over an extended epoch. The constant level of precision with this target further suggests that functional benefits of fixational eye movements (Tulunay-Keesey, 1960) are preserved. We envision that our novel fixation target may be useful in applications where maintaining gaze over long durations is critical, for example during visual field testing, experiments in vision science, or for individuals with impaired central vision (e.g. age-related macular degeneration) when viewing with an eccentric retinal locus.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.